mention NVN usage in contributing guide

CONTRIBUTING.md

@@ -84,6 +84,12 @@ You can immediately start working on the code using [a pre-setup Gitpod environm
 * Switch to the most recent Node LTS (you should be able to use older/newer versions of Node but we recommend to use v18 LTS so all developers are on the same side) or to the one denoted in `.nvmrc`. We recommend to use [`nvm`](https://github.com/nvm-sh/nvm) to switch between Node.js versions.
 
 * Set up the project:
+    First make sure you have the right Node.js version installed. You can find the current defined development version in `.nvmrc` within the root directory of the project. The easiest way to handle multiple Node.js versions is by using [NVM](https://github.com/nvm-sh/nvm). After it is installed you can run:
+    ```sh
+    $ nvm install
+    ```
+
+    This will install the defined Node.js version for you. You can then go ahead and set-up the project via:
 
     ```sh
     $ npm install